1. Field of the Invention
The present invention relates to a recoding apparatus for performing recording on a recording medium by means of bidirectional recording obtained by superposing recording based on a forward stroke of a recording head (hereinafter referred to as “forward recording”) on recording based on a backward stroke of the recording head (hereinafter referred to as “backward stoke recording”), and a reciprocating record position alignment method for aligning the record position of the backward recording relative to the forward stoke recording in the recording apparatus.
2. Description of the Related Art
A recording apparatus (so-called bidirectional recording printer) for performing recording on a recording medium in such a manner that a recording head having ink jet nozzles is reciprocated by a carriage to superpose recording based on a forward stroke of the recording head and recording based on a backward stroke of the recording head on each other has been heretofore put into practical use.
In this type printer for performing bidirectional recording, there is however a problem that record position displacement (print position displacement) occurs between the forward recording and the backward recording. The record position displacement is caused by the following factors: backlash of a carriage drive mechanism at the time of forward movement and at the time of backward movement; positional displacement between the forward record position where ink jetted at the time of forward stoke recording (forward printing) is deposited on a sheet and the backward record position where ink jetted at the time of backward recording (backward printing) is deposited on the sheet; delicate difference between the forward recording speed and the backward recording speed; etc.
Therefore, various inventions have been already proposed to eliminate the aforementioned record position displacement.
For example, in JP-A-2000-037937, there has been proposed a print position alignment method and a printing apparatus in which check patterns (patches) obtained by changing the record position of backward recording relative to forward recording by a predetermined amount successively are recorded as check patterns (patches) recorded by means of bidirectional recording so that an optimum record position (optimum print position) is determined on the basis of respective density data of the check patterns (patches). More specifically, density data of each check pattern (patch) are measured at a plurality of points (e.g. 12 points) and the average of the density data is computed (calculated), so that the record position where density is the highest is selected as an optimum record position (optimum print position) on the basis of the relation between the record position condition and the average of the density data.
When the average of density data at the plurality of points (12 points) is computed (calculated), a difference between the minimum and the maximum of the density data is calculated in accordance with each check pattern (patch). When the difference is larger than a predetermined threshold, a decision is made that density unevenness occurs, so that an optimum print position is determined in the condition that the density data of the check pattern (patch) are removed.
JP-A-2000-037937 (especially, paragraph numbers [0109] to [0112]) is referred to as a related art.
In the record position alignment method according to the background art, the optimum record position is however determined on the basis of density data at a plurality of points without consideration of the measurement position of the density data in each check pattern (patch). Accordingly, there is a problem that a determination result different from a determination result based on human eye observation may be deduced.
That is, when a check pattern (patch) in which adjacent density data changes slowly is determined by human eye observation, a decision may be made that there is no displacement in record position if the amount of variation in adjacent density data is small. In this case, the check pattern may be determined to be the check pattern optimized in record position (the best check pattern). Even in such a check pattern, if the difference between density data measured at positions far from each other is large, a decision may be however made that there is density unevenness. Accordingly, the check pattern is not determined to be the best check pattern by the background art method.
When density data partially varies widely according to the influence of temporary noise or the like but there is no displacement in record position as an overall record state of the check pattern, a determination by human eye observation may make a decision that there is no displacement in record position. In this case, the check pattern may be determined to be the best check pattern. Even in such a check pattern, if the difference between density data in the noise portion and density data in the other portion is large, the background art method however makes a decision that there is density unevenness. In this case, the check pattern is not determined to be the best check pattern.
On the other hand, when a check pattern in which the difference between the maximum and minimum values of density data is not large but the amount of variation of density data at adjacent detection places is large is determined by human eye observation, a decision may be made that there is any displacement in record position. Even in such a check pattern, if the difference between the maximum and minimum values of density data is smaller than that of any other check pattern, the background art method may judge the check pattern to be the best check pattern.
As described above, when a result of determination is different from a result of determination by human eye observation, there is a problem that a resulting image recorded in a record position set on the basis of the determination result is felt to be inappropriate to human beings because of displacement in record position.